This is not possible. There used to be an option to hide extensions, but this was removed in Firefox 3.6 to prevent extensions from being installed in such a way that the user might not be able to tell they're installed.

This is not possible. There used to be an option to hide extensions, but this was removed in Firefox 3.6 to prevent extensions from being installed in such a way that the user might not be able to tell they're installed.